Why do my hair particles disappear when physics is set to None
Different particle systems:
A &quot;regular particle system&quot; is of type Emitter and spawns particles which hava a size, different modes of display (object instancing etc) and move according to the selected form of physics simulation.
A Hair particle system is not identical to that, since Hair particles require a different set of information; they have a root connecting them to the emitter and are path objects, which can be physically simulated as well - this is what the Hair Dynamics option is for.
As long as you don't enable Hair Dynamics, your particles shouldn't move or collide, regardless of the selected Physics option.
Hair particles require a velocity. Tweaking it will result in a different size, which should correlate to your observation regarding timesteps: changing the speed by which time passes changes all velocities. A hair particle with a velocity of zero has a length of zero, so setting the Physics type to &quot;None&quot; is a bad idea; it means we are creating particles without speed and therefor without length.